Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0301, P0302, P0303, P0304, P0305, P0306 [AJ] DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED Have FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (Misfire related) been recorded?	Yes	Go to the next step.
1		No	Record FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS on repair order, then go to the next step.
2	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Check for related Service Bulletins and/or online repair information availability. Is any related repair information available?	Yes	Perform repair or diagnosis according to the available repair information. If the vehicle is not repaired, go to the next step.
2		No	Go to the next step.
3	VERIFY RELATED PENDING CODE OR STORED DTCs Turn ignition switch to OFF then ON (Engine off). Verify related pending code or stored DTCs. Is other DTCs present?	Yes	Go to appropriate DTC troubleshooting. (See DTC TABLE .)
3		No	Go to the next step.
4	VERIFY CURRENT INPUT SIGNAL STATUS (KEY TO ON/IDLE) Access APP1, APP2, ECT, IAT, MAF, RPM TP_REL and VSS PIDs using the WDS or equivalent. (See PCM INSPECTION .) Is there any signal that is far out of specification when ignition switch is ON and engine runs at idle?	Yes	Inspect suspected circuit or part or both according to inspection results. Then go to Step 13. (See PCM INSPECTION .)
4		No	Go to the next step.
5	VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION Inspect same PIDs as in Step 4 when simulating FREEZE FRAME DATA condition. Is there any signal which causes drastic changes?	Yes	Inspect suspected circuit or part or both according to inspection results. Then go to Step 13. (See PCM INSPECTION .)
5		No	Go to the next step.
6	INSPECT SPARK PLUG CONDITION Turn the ignition switch off. Remove spark plug from suspected cylinder. Check spark plug condition: Cracks Excess wear Gap Wet Is any problem found on spark plug?	Yes	If spark plug is wet, fuel flooding is suspected. Go to step 9. If spark plug has a crack, excess wear or improper gap, replace faulty spark plug. Then go to Step 13. (See SPARK PLUG REMOVAL/INSTALLATION .)
6		No	Go to the next step.
7	INSPECT IGNITION SYSTEM OPERATION FOR SUSPECTED CYLINDER Perform Spark Test for suspected cylinder. (See SPARK TEST .) Is result of Spark Test normal?	Yes	Go to the next step.
7		No	Replace or replace malfunctioning part according to spark test results, then go to Step 13.
8	INSPECT FUEL INJECTOR HARNESS Remove intake air system parts. Disconnect fuel injector connector on suspected cylinder. Connect noid light to fuel injector connector terminals. Check light dimness during cranking. Does noid light illuminate?	Yes	Go to the next step.
8		No	Check fuel injector harnesses. Repair or replace it if necessary, then go to Step 13.
9	INSPECT FUEL INJECTOR OPERATION Remove fuel injector from suspected cylinder. (See FUEL INJECTOR REMOVAL/INSTALLATION [AJ] .) Swap injector with injector on other cylinder. Start engine and run it at idle. Is there misfire DTC for the cylinder which has a suspected fuel injector?	Yes	Replace injector, then go to step 13. (See FUEL INJECTOR REMOVAL/INSTALLATION [AJ] .)
9		No	Go to the next step.
10	INSPECT FOR AIR SUCTION AT INTAKE AIR SYSTEM Inspect for air leakage at the following: Around connection of dynamic chamber and intake manifold Around connection of intake manifold and cylinder head Is air leakage found?	Yes	Repair or replace suspected part, then go to Step 13.
10		No	Go to the next step.
11	INSPECT SEALING OF ENGINE COOLANT PASSAGE WARNING: Removing radiator cap when radiator is hot is dangerous, Scalding coolant and steam may shoot out and cause serious injury. When removing radiator cap, wrap thick cloth around and turn it slowly. Remove radiator cap. Implement procedure to bleed air from engine coolant, then run engine at idle. Are there any small bubbles which make engine coolant white at filling opening? NOTE: Large bubbles are normal since they are remaining air coming out from engine coolant passage.	Yes	Air gets in from poor sealing of head gasket or other areas between combustion chamber and engine coolant passage. Repair or replace faulty parts, then go to Step 13.
11		No	Go to the next step.
12	INSPECT ENGINE COMPRESSION Inspect engine compression. (See COMPRESSION INSPECTION .) Is engine compression normal?	Yes	Go to the next step.
12		No	Overhaul the engine, then go to the next step.
13	VERIFY TROUBLESHOOTING OF MISFIRE DTC COMPLETED Make sure to reconnect all disconnected connectors. Start engine. Clear the DTC from the PCM memory using the WDS or equivalent. Perform DRIVE MODE 1. (See OBD-II DRIVE MODE .) Is PENDING CODE same as DTC present?	Yes	Replace PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION .)
13		No	Go to the next step.
14	VERIFY AFTER REPAIR PROCEDURE Perform "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE .) Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE .)
14		No	Troubleshooting completed.